There’s nothing like a food diary to keep you honest about what you eat. That’s the idea behind The Eatery, an iPhone app that asks you to snap a picture of your food, and provides you with a healthiness meter that rates not just your current meal, but your noshing habits over time.

The Eatery dubs itself “A Massive Health Experiment” and gives us an unprecedented window into what people like to eat, all over the world. Whether you’re a foodie in France or a pathological snacker in San Francisco, if you take a picture of your food, you’ve become part of the experiment.

With platefuls of data now collected, some global eating patterns are starting to emerge. Based on a review of five months worth of food images, San Franciscans, for example, eat 4.4 times more Brussels sprouts and 3.4 times more cashews than people in other cities. New Yorkers eat twice as much oatmeal and down and 6.7 times more coffee than other city dwellers.

Globally, you might interested to know that compared to people elsewhere, folks living in Copenhagen eat 18.5 times more rye, Sao Paolo residents eat 9.5 times more papaya, and people in Tokyo, where sushi is one the more popular meals, consume nearly four times more fish.

Based on the app’s average fit-vs.-fat rating of foods, the data also provide a health rating for each city: New York receives an impressive 83.6% despite its plethora of rich, gourmet fare and abundant fast food, while Tokyo ranked a surprisingly low 30.3% (the app’s data crunchers aren’t sure why).

Ultimately, the goal of The Eatery, says Andrew Rosenthal, chief strategy officer of Massive Health, the company that developed the app, is to give people a leg up on eating better. After all, eating is not just about counting calories, it’s also about knowing what you tend to eat when, and what triggers certain unhealthy dietary habits. Understanding your weaknesses when it comes to food can go a long way toward helping you change your fattening ways.

The key to the app is other users, who keep you honest. You snap a picture of whatever you eat, give it a label, like “vegetable pizza” or “iced tea,” and rate it on a fit-to-fat scale. It’s not scientifically based, since people’s subjective evaluations of their food vary, but taken together, the ratings turn out to be pretty accurate.

As soon as you post your image, other users give their own fit-fat ratings of what you’re eating. (On average, with hundreds of thousands of users, and eight million food ratings, you can expect about 20 people to rate your lunchtime panini in five minutes or less.) Based on the data the company has gathered so far, it seems that other people are generally better at rating the healthiness of your meals than you are. That means that I’m consistently giving my pizza a healthier ranking than others are, so over time, I may come to realize that I’m not being honest with myself about how nutritious my diet is.

Not surprisingly, the discrepancy is greatest for unhealthy foods, Rosenthal says, suggesting that many of us are in denial about eating our favorite fatty, calorie-heavy foods. At the top of the list of foods with the biggest rating gap by eaters and other raters: bacon, of course. People eating bacon consistently rate it three times healthier than others do.

Once the app has enough users, Rosenthal says, the data will be able to bear out stronger trends that can be translates into personalized action plans to help people eat better. Since the app can track the average fit-fat ratings of your diet, it can tell you with how well you ate today compared to yesterday, or this week versus last week. Based on that information, the app can also pick out what contributed to your better or worse eating habits — noting, for example, that about half the time you grab coffee for breakfast, you’re also getting a muffin, which could be sabotaging your effort to stay slim.

“We want to be able to get to the point where we can tell people what the one thing they should do [to eat healthier] is,” he says. “It’s about using the data to be meaningful and giving people actionable feedback.”

So far, Rosenthal says, The Eatery app appears to be helping. People relying on the app for 30 days averaged an 8% improvement in eating on the fit-fat scale, and those sticking with the app for 90 days improved 11%.

For now, the ratings offer only a very rough cut of how healthy or nutritious a particular foods are, but eventually, says Rosenthal, the company hopes to add more precise information about calories and nutrients. More detailed analyses of your lunch means no more denial about exactly how healthy for you that Caesar salad with dressing really is.

Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.